Chapter X: The Order Rodentia (2)

The circumstance which has given more popular interest to the Lemming than to a host of other species of the same order of animals is that certain districts of the cultivated lands of Norway and Sweden, where in ordinary circumstances they are quite unknown, are occasionally and at very uncertain intervals, varying from five to twenty or more years, literally overrun by an army of these little creatures, which steadily and slowly advance, always in the same direction, and regardless of all obstacles, swimming across streams and even lakes of several miles in breadth, and committing considerable devastation on their line of march by the quantity of food they consume. In their turn they are pursued and harassed by crowds of beasts and birds of prey, as bears, wolves, foxes, dogs, wild cats, stoats, weasels, eagles, hawks, and owls, and never spared by man; even the domestic animals not usually predaceous, as cattle, goats, and reindeer, are said to join in the destruction, stamping them to the ground with their feet, and even eating their bodies. Numbers also die from diseases apparently produced from overcrowding. None ever return by the course by which they came, and the onward march of the survivors never ceases until they reach the sea, into which they plunge, and swimming onwards in the same direction as before perish in the waves. These extraordinary and sudden appearances of vast bodies of Lemmings, and their singular habit of persistently pursuing the same onward course of migration, have given rise to various speculations, from the ancient belief of the Norwegian peasants, shared in by Olaus Magnus, that they fall down from the clouds, to the almost equally untenable hypothesis, ingeniously maintained by the late Mr. W. D. Crotch, that they are acting in these migrations in obedience to an instinct inherited from vastly ancient times, and are still seeking the congenial home in a supposed submerged Atlantis, to which their ancestors of the Miocene period were wont to resort when driven from their ordinary dwelling-places by crowding or scarcity of food. The principal really ascertained facts regarding these migrations seem to be as follows. When any combination of circumstances has occasioned an increase in the numbers of the Lemmings in their ordinary dwelling-places, impelled by the restless or migratory instinct possessed in a less developed degree by so many of their congeners, a movement takes place at the edge of the elevated plateau, and a migration towards the lower-lying land begins. The whole body moves forward slowly, always advancing in the same general direction in which they originally started, but following more or less the course of the great valleys. They only travel by night; and, staying in congenial places for considerable periods, with unaccustomed abundance of provender, notwithstanding all the destructive influences to which they are exposed, they multiply excessively during their journey, having families still more numerous and more frequently than in their usual homes. The progress may last from one to three years, according to the route taken, and the distance to be traversed until the sea-coast is reached, which in a country so surrounded by water as the Scandinavian peninsula must be the ultimate goal of such a journey. This may be either the Atlantic or the Gulf of Bothnia, according as the migration has commenced from the west or the east side of the central elevated plateau. Those that finally perish in the sea, committing what appears to be a voluntary suicide, are only acting under the same blind impulse which has led them previously to cross smaller pieces of water with safety.

_Cuniculus._[346]—Cranial and incisive characters those of _Myodes_, in the main, but the molars more of an Arvicoline type, the first upper one differing from that of all other members of the family in having seven prisms. Externally of the general shape of _Myodes_, but distinguished by the absence of external ears, the shortness and dense furring of the feet, the obsolete pollex with rudimentary nail, and the great length of the two middle claws of the manus. Represented by one species, the Banded Lemming (_C. torquatus_), of the Arctic region.

Remains of both _C. torquatus_ and _Myodes lemmus_ occur in British Pleistocene deposits.

_Fiber._[347]—Closely allied to _Arvicola_, both externally and in cranial and dental characters, but with the tail nearly as long as the body (apart from the head), compressed, nearly naked, and reticulate. Feet incompletely webbed, and the whole body adapted for a thoroughly aquatic life.

The Musk-Rat or Musquash (_F. zibethicus_, Fig. 209) is the only representative of this genus, and the largest member of the subfamily, the head and body being about 12 inches in length. It is rather a heavily built animal, with a broad head, no distinct neck, and short limbs; the eyes are small, and the ears project very little beyond the fur. The fore limbs have four toes and a rudimentary thumb, all with claws; the hind limbs are larger, with five distinct toes, united by short webs at their bases. The tail is laterally compressed, nearly naked, and scaly. The hair much resembles that of a beaver, but is shorter; it consists of a thick soft under-fur interspersed with longer stiff, glistening hairs, which overlie and conceal the former on the upper surface and sides of the body. The general colour is dark umber-brown, almost black on the back and gray below. The tail and naked parts of the feet are black. The musky odour from which it derives its name is due to the secretion of a large gland situated in the inguinal region, and present in both sexes.

The Musk-Rat is peculiar to America, being extensively distributed in suitable localities in the northern part of the continent, extending from the Atlantic to the Pacific, and from the Rio Grande to the barren grounds bordering the Arctic Seas. It is aquatic in its habits, living on the shores of lakes and rivers, swimming and diving with great facility, feeding on the roots, stems, and leaves of water-plants, or on fruits and vegetables which grow near the margin of the streams it inhabits. Musk-Rats are most active at night, spending the greater part of the day concealed in their burrows dug out of the bank, consisting of a chamber with numerous passages, all of which open under the surface of the water. For winter quarters they build more elaborate houses of conical or dome-like form, composed of sedges, grasses, and similar materials plastered together with mud. As their fur is an important article of commerce, large numbers are annually killed, being either trapped or speared at the mouths of their holes.

The skull of the Musk-Rat is shown in Fig. 203 (p. 459); its structure is essentially Arvicoline, but the squamosals are greatly expanded, with a corresponding reduction of the parietal and interparietal, and the interorbital constriction of the frontals attains its greatest development. Fossil remains of _Fiber_ occur in the North American Pleistocene.

_Neofiber._[348]—This genus, while agreeing with _Fiber_ in the characters of the skull and teeth, differs by the cylindrical tail, and the normal form of the feet, in which the toes are not bent laterally at an angle with the sole. The single species _N. alleni_, commonly known as the Round-tailed Musk-Rat, is found in Florida, and is much less completely aquatic in its habits than _Fiber_. Its colour is brown above, and silvery-white mixed with rufous below, the sides of the body gradually shading from brown to rufous, the forehead and the tip of the nose are black, while the tail is rufous mingled with black.

Subfamily =Siphneinæ=.—Includes two genera of Mole-like Rodents with an _Arvicoline_ dentition, but with the body thoroughly adapted for a subterranean life, the limbs and tail being very short, and the external ears rudimentary. Both are Palæarctic.

_Ellobius._[349]—The Russian _E. talpinus_, the typical representative of the genus, has short claws, and comes nearest to the _Arvicolinæ_. _E. fuscocapillus_ is from Afghanistan.

_Siphneus._[350]—This genus (Fig. 210) includes species inhabiting Northern and Central Asia, and is characterised by the great length of the claws of the manus. Remains of an existing species occur in the Pleistocene of the Altai, while an extinct one has been described from the Pliocene of North China.

Subfamily =Deomyinæ=.—Represented only by the under-mentioned genus, in which the bituberculate anterior and tricuspidate middle ridge of the first upper molar presents a condition intermediate between that obtaining in the _Cricetinæ_ and that of the _Murinæ_.

_Deomys._[351]—Externally as in _Mus_. Pollex with a narrow nail; hind feet elongate. Infraorbital vacuity of skull triangular, not narrowed below. Upper incisors with a pair of minute grooves. First upper molar with seven distinct tubercles, of which three are placed on the middle ridge, and two on each of the others. One species, _D. ferrugineus_, from the Lower Congo, an animal about the size of the Common Mouse.

Subfamily =Murinæ=.—Molars rooted and tuberculated; those of the upper jaw with three longitudinal rows of tubercles (Fig. 206, _A_).

This group includes the true Rats and Mice, and may be regarded as more specialised than the _Cricetinæ_. All the members of the group closely resemble one another, and are light and active, with large ears, bright eyes, and long and scaly tails. Their coloration, in conformity with the fossorial and nocturnal habits of most of the forms, is sombre, and their movements are remarkably agile and graceful.

_Mus._[352]—Incisors narrow, without grooves. Structure of molars as in Fig. 206, _A_ (p. 463). Incisive foramina of skull long; coronoid process of mandible well developed. Ears and eyes large; muzzle naked at the extremity. Fur soft, in some cases intermingled with spines. Pollex with a short nail in place of a claw. No cheek-pouches. Tail long, nearly naked, with rings of overlapping scales. Vertebræ: C 7, D 13, L 6, S 4, C 26-32.

This genus is the largest in the whole mammalian class, comprising not less than 130 species, ranging over the whole of the Old World, with the noteworthy exception of Madagascar. On the whole, the species are more numerous in tropical than in temperate regions, and very few occur in cold countries. Many of the species living in warm climates have flattened spines mingled with the fur; these spines being shed in winter, when a warmer covering is necessary, and replaced by hair. Five species occur in England, which are briefly noticed below; and it may be observed that none of the species are much larger than _M. decumanus_ or smaller than _M. minutus_. As a rule the habits of the species are similar to those of the English forms, but a few are arboreal, while others again, like the one represented in Fig. 211, are aquatic. The earliest known representatives of the genus (excluding _Acanthomys gaudryi_ of the Lower Pliocene Pikermi beds of Attica) occur in the Pleistocene of Europe.

The Brown or Norway Rat (_M. decumanus_) is a heavily built animal, growing to 8 or 9 inches in length, with a bluff rounded head, small ears (Fig. 212, _A_), and a comparatively short tail, which is always shorter than the head and body combined, and generally not longer than the body alone. The colour is a uniform grayish-brown above and white below, the ears, feet, and tail being flesh coloured. Black varieties, which are often mistaken for true Black Rats, are by no means rare, but the differences in size and proportions form a ready means of distinguishing the two. The Brown Rat is believed to be a native of Western China, where a race (_M. humiliatus_) has been discovered so like it as to be practically indistinguishable. Both this, and the next species agree in their predaceous habits, omnivorous diet, and great fecundity. They bear four or five times in the year from four to ten blind and naked young, which are in their turn able to breed at an age of about six months; the time of gestation being about twenty days.

The Black Rat (_M. rattus_) is a smaller and more lightly built species, generally not more than 7 inches in length, with a slender head (Fig. 212, _B_), large ears, and a thin tail of about 8 or 9 inches in length. The colour is usually a glossy bluish-black, somewhat lighter below; but in the tropical variety described as _M. alexandrinus_ the general colour is gray or rufous, and the belly white. The disposition of the Black Rat is milder than that of _M. decumanus_, and the white and pied rats kept as pets mostly belong to this species. In many localities where it was formerly abundant it has been entirely superseded by _M. decumanus_, but it is said that in some parts of Germany it has been lately reasserting itself.

_M. musculus_, the Common House-Mouse, is, like the Brown Rat, originally a native of Asia, whence it has spread to all the inhabited parts of the globe. Its habits and appearance are too well known to need any description.

_M. sylvaticus_, the Wood or Long-tailed Field-Mouse, is very common in many parts of England, often taking to barns and outhouses for shelter during the winter. It is of about the same size and proportions as _M. musculus_, but of a bright reddish-gray colour, with a pure white belly.

_M. minutus_, the Harvest-Mouse, is the smallest of the European Mice, seldom exceeding 2½ or 3 inches in length. It is of a yellowish-red colour, with comparatively short ears and tail. It lives entirely away from human habitations, generally dwelling in grass or corn-fields, where it builds a globular nest of dried grass of the size of a cricket-ball, in which the young are nurtured.

_Nesocia._[353]—General characters those of _Mus_, but the incisors and molars very much wider, and the tubercles of the latter more connected by transverse ridges, thus producing a laminated type of structure.

This genus has been placed by some writers in a distinct subfamily with _Phlœomys_, but Mr. O. Thomas regards it as so closely allied to _Mus_ that even its generic separation may be open to question. It comprises several species, mostly spread over Southern Asia, ranging from Palestine to Formosa, and from Kashmir to Ceylon, but _N. scullyi_ is found in Turkestan. The great Indian Bandicoot-Rat (_N. bandicota_) is the largest representative of the subfamily, often exceeding a foot in length. _N. bengalensis_ is remarkable for possessing no less than eighteen mammæ. Fossil remains of _Nesocia_ occur in the Pleistocene of Madras and in the Pliocene of Northern India; those from the first-named deposits being referable to existing species.

_Golunda._[354]—Like _Mus_, but with a distinct groove down the front of the upper incisors. There are only three species, one from Western India, one from West Africa, and the other from Eastern Africa.

_Uromys._[355]—Differs from _Mus_ in having the scales of the tail not overlapping, but set edge to edge, so as to form a sort of mosaic work. There are about six species of _Uromys_, spread over the northern part of the Australian region from the Aru Islands to Queensland.

_Chiruromys._[356]—Externally like _Mus_, but with the terminal portion of the tail without scales above, quite naked, transversely wrinkled, and prehensile. Scales of remainder of tail more or less pentagonal, and arranged in oblique diagonal series. Supraorbital vacuity of skull without projecting plate in external wall. Incisive foramina short and narrow; auditory bulla small. Upper molars very complex, with the tubercles (of which there are eleven in the first tooth) low, and distinctly arranged in transverse rows. Known only by _C. forbesi_, from mountains in New Guinea, which must be regarded as a specialised form very similar in outward appearance to _Uromys cervinipes_.

_Hapalotis._[357]—Hind limbs elongated. Incisive foramina very large. No coronoid process to the mandible. This genus is confined to Australia, where there are about fifteen species known. They are pretty little animals, with long ears and tail, and in many respects resemble the Jerboas, whose place they seem to take in the sandy Australian deserts. Remains of _H. albipes_ occur in the Pleistocene of New South Wales.

_Mastacomys._[358]—Like _Mus_, but with the molars remarkably broadened, and with only four mammæ. The single species of the genus is as yet only known from Tasmania, though it has been found fossil in New South Wales; it is somewhat similar in size and general appearance to the English Water-Vole, but has much longer and softer fur.

_Acanthomys._[359]—Fur almost entirely composed of flattened spines. Teeth and skull as in _Mus_, but the coronoid process of mandible very small. There are six species of Spiny-Mice known, all of about the size of the Common Mouse. They are found in Syria, Palestine, and Eastern Africa as far south as Mozambique. _A. dimidiatus_ presents the appearance of a little Hedgehog when its spines are erected; it inhabits the stony deserts of Arabia Petræa and Palestine, and feeds on bulbs. A fossil Mouse (_A. gaudryi_) referred to this genus occurs in the Lower Pliocene of Attica.

_Echinothrix._[360]—A very remarkable rat with an extremely elongated muzzle, all the bones of the face being much produced. The incisors are faintly grooved. The only species is _E. leucura_, an animal of about the size of the Brown Rat, with its fur thickly mixed with spines. It is found in Celebes.

_Typhlomys._[361]—This genus is represented by a single species from China, which resembles a House-Mouse in size and general appearance, but has smaller ears, while the eyes are so reduced in size as to be totally concealed by the long eyelashes.

_Cricetomys_[362] and _Saccostomus_.[363]—These two African genera have been—from the presence of cheek-pouches—usually placed in the neighbourhood of _Cricetus_, but their molars are of the Murine type. _Cricetomys_ is said to have grooved upper incisors, and is represented only by _C. gambianus_. There are two species of _Saccostomus_.

_Pithechirus._—A small Rodent from Sumatra and Java described under this name is a true Mouse, having nothing to do with _Chiropodomys_, to which it has been compared.

_Family_ SPALACIDÆ.

Mole-like forms, with very small or rudimentary eyes and ear-conchs, large claws, and short or rudimentary tail. Form cylindrical. Incisors large; premolars present or absent; molars rooted, with re-entering enamel-folds; palate narrow.

Subfamily =Spalacinæ=.—Angular part of the mandible arising from the lower edge of the socket of the lower incisor. No premolars.

_Spalax._[364]—Represented by the great Mole-Rat (_S. typhlus_) of South-Eastern Europe, in which the eyes are completely covered by the skin.

_Rhizomys._[365]—Eyes uncovered, although very minute; small naked ear-conchs; and a short partially hairy tail. Includes several species from Northern India, Tibet, China, Burma, Malaya, and Eastern Africa. A fossil species occurs in the Pliocene Siwaliks of Northern India.

Subfamily =Bathyerginæ=.—Angular part of the mandible arising from the side of the socket of the lower incisor. Premolars absent or present. Confined to the Ethiopian region.

_Bathyergus._[366]—Upper incisors strongly grooved; _p_ ¹⁄₁, _m_ ³⁄₃; no ear-conchs; very powerful claws. One species (_B. maritimus_), from South Africa, attaining a length of about 10 inches.

_Georychus_[367] and _Myoscalops_.[368]—Upper incisors without grooves. _Georychus_, with some half dozen species, generally has _p_ ¹⁄₁; _Myoscalops_, with one species, usually has _p_ ³⁄₃, and the second toe of the foot is the longest. In _Georychus_ the premolar may be wanting, and some examples of _Myoscalops_ have only two teeth of this series.

_Heterocephalus._[369]—Small and nearly naked forms, with small head, small eyes, no ear-conchs, moderately long tail, and powerful fore feet provided with a pair of large pads; _p_ ⁰⁄₀, _m_ ²⁻³⁄₂₋₃. Two species. These very remarkable little Rodents are regarded by Mr. O. Thomas as very closely allied to _Georychus_, but specialised, and, so to speak, somewhat degraded for a purely subterranean life, for which their hairless body is peculiarly adapted. They are found in Somali-land, where they burrow in the sandy soil.

_Family_ GEOMYIDÆ.[370]

Terrestrial or fossorial forms, with large cheek-pouches opening on the cheeks outside the mouth. Squamosal much expanded, and the jugal extending forwards to the lachrymal. _P_ ¹⁄₁; molars rooted or rootless, with transverse laminæ. Nearctic and Neotropical regions.

Subfamily =Geomyinæ=.—Incisors broad; mastoid not appearing on the top of the skull; eyes small; ear-conch rudimentary; limbs short, subequal. Habits fossorial.

_Geomys._[371]—Upper incisors deeply grooved. The common North American Pouched-Rat or “Pocket-Gopher” (_G. bursarius_) inhabits the plains of the Mississippi and lives in burrows. Several other species are recognised from the Southern United States, Mexico, and Central America. The genus is represented in the Pleistocene and Pliocene of the United States.

_Thomomys._[372]—Upper incisors plain. Represented by two species, with numerous varieties found all over Canada and North America west of the Rocky Mountains. Remains referred to an existing species occur in the Pliocene of Oregon. _Entoptychus_, from the Miocene of the United States, is an allied genus, with broad incisors and rootless molars.

Subfamily =Heteromyinæ=.—Incisors narrow; mastoid appearing largely on the top of the skull; eyes and ears moderate or large; hind limbs and tail elongated. Habits terrestrial.

_Dipodomys._[373]—This genus is characterised by the rootless molars. It is best known by _D. phillipsi_, the Kangaroo-Rat of the desert regions east of the Rocky Mountains, having habits like those of the Jerboas. The typical forms have four toes in the pes; but in others, which it has been proposed to separate as _Dipodops_, there are five: _D. ordi_ and _D. agilis_ belong to the latter group.

_Perognathus_[374] and _Heteromys_.[375]—In both these genera, which are represented by species of very small size, the molars are rooted; the latter being distinguished by the presence of flattened spines mingled with the fur, and having species ranging into South America. According to Dr. C. H. Merriam the forms described as _Cricetodipus_ are not separable from _Perognathus_; while Dr. Coues considers that _Saccomys_ was founded upon a species of _Heteromys_. _Pleurolichus_, from the Miocene of the United States, is regarded as an extinct genus allied to _Heteromys_.

_Family_ DIPODIDÆ.

Terrestrial forms usually with four upper cheek-teeth, and typically with the following characters. Incisors compressed; molars with transverse enamel-folds; infraorbital vacuity of skull (Fig. 7, p. 37) large and rounded; jugal ascending in front to the lachrymal; and the mastoid part of the auditory bulla usually very large.

Subfamily =Sminthinæ=.—Molars rooted; _p_ ¹⁄₀, _m_ ³⁄₃. Skull with the infraorbital vacuity widest below, and the incisive palatal foramina long. Limbs short. Palæarctic.

_Sminthus._[376]—Represented by the Rat-like _S. vagans_ from Northern Europe and Asia, in which the ears are rather long and pointed, the tail is covered with short hairs and nearly as long as the body, while the molars present a somewhat complicated pattern. This genus has generally been regarded as an aberrant member of the _Muridæ_, but was transferred in 1887 to the present family by Dr. H. Winge.

Subfamily =Zapodinæ=.—Molars rooted; _p_ ¹⁄₁, _m_ ³⁄₃; cervical vertebræ free; hind limbs elongated; metatarsals separate; hind feet with five digits. Nearctic region.

_Zapus._[377]—The American Jumping-Mouse (_Z. hudsonianus_) extends over almost the whole North-American continent from Labrador to Mexico.

Subfamily =Dipodinæ=.—Molars rooted; _p_ ⁰⁻¹⁄₀₋₁, _m_ ³⁄₃; cervical vertebræ more or less ankylosed; hind limbs elongated; metatarsals united; hind feet with only three functional digits. Palæarctic and Ethiopian regions.

This subfamily includes the true Jerboas, and contains three genera: _Dipus_[378] with three toes, and _Alactaga_[379] and _Platycercomys_[380] with five, the outer two not reaching to the ground. The latter is distinguished by the absence of premolars, and comprises many species extending from Siberia to Nubia.

Remains of the existing _Alactaga decumana_[381] occur in the Pleistocene of Germany, and those of _Zapus hudsonianus_ in the corresponding strata of the United States. _Platycercomys_ has been recorded from the Pleistocene of Northern Asia.

Subfamily =Pedetinæ=.—Molars rootless; cervical vertebræ free; hind limbs elongated; metatarsals separate; hind feet with four digits. Vertebræ: C 7, D 12, L 7, S 3, C 30. Ethiopian region.

_Pedetes_,[382] the Cape Jumping-Hare (_P. caffer_), by far the largest species of the family, extends from Mozambique and Angola to the Cape of Good Hope.

_Section_ HYSTRICOMORPHA.

Skull (Fig. 213) with a stout zygomatic arch; jugal not supported below by a continuation of the maxillary zygomatic process; infraorbital vacuity large; mandible with the angular part arising from the outer side of the bony socket of the lower incisor. Clavicles perfect or imperfect; fibula distinct. One premolar in each jaw.

_Family_ OCTODONTIDÆ.

Clavicles complete. Skull with long incisive foramina extending into the maxillæ; and usually an inferior angle to the jugal. Molars with external and internal enamel-folds; _p_ ¹⁄₁, except in _Ctenodactylus_. Mammæ placed high up on the sides of the body. Confined to the Ethiopian and Neotropical regions, with the exception of one species of _Echinomys_ which ranges into Central America. Habits mostly terrestrial, but occasionally fossorial or natatorial.

Subfamily =Ctenodactylinæ=.—Molars semi-rooted; jugal as in _Dipodidæ_; the two inner toes of the hind feet with a horny comb and rigid bristles. Ethiopian region.

_Ctenodactylus._[383]—Represented only by _C. gundi_ from North Africa, on the borders of the Sahara. Has no premolars; each foot has four digits; the hind limbs are rather longer than the fore; the ears small; and the tail reduced to a stump. This animal is about the size of the Water-Vole, and dwells on rocky ground, its habits being diurnal. The peculiar comb-like inner toes are employed for dressing the fur.

_Pectinator._[384]—Closely allied to the preceding, but with a minute premolar in each jaw; and a moderately long and bushy tail. One species (_P. spekei_), from Somali-land.

Subfamily =Octodontinæ=.—Molars semi-rooted or rootless, with simple enamel-folds; fur soft. There are some six existing genera, including Rat-like species, all of which are South American, except _Petromys_, which is Ethiopian.

_Octodon._[385]—Upper and lower molars alike; ears moderate; tail of medium length and tufted. Vertebræ: C 7, D 12, L 7, S 4, C 25. Typically represented by _C. cumingi_ of Chili and Peru, with other species from Chili and Bolivia. They live in large communities.

_Habrocoma._[386]—Lower molars more complex than the upper; ears large; and fur extremely soft. Two Bolivian species.

_Schizodon._[387]—One species, inhabiting elevated spots in the Southern Andes, and characterised by the enamel-folds of the upper molars meeting in the middle line. The external characters are much the same as in _Ctenomys_, but the ears are larger and the claws shorter.

_Ctenomys._[388]—Incisors broad; molars rootless, with kidney-shaped crowns; last molar small and cylindrical; eyes and ears very small; claws larger than the toes. Some four species. Fossil remains are common in the Pleistocene of Buenos Ayres and the cavern-deposits of Brazil. Habits fossorial.

_Spalacopus._[389]—Represented by two Chilian species, distinguished from the preceding genus by the rudimentary ears. These rodents store up magazines of food in their burrows.

_Petromys._[390]—The South African _P. typicus_ is closely allied to _Spalacopus_, but differs by its harsh fur, the shortness of the pollex, and the somewhat bushy tail. The teeth are semi-rooted, with single inner and outer enamel-folds, nearly meeting in the middle.

Subfamily =Echinomyinæ=.—Molars semi-rooted or rootless, with deep and curved enamel-folds; fur more or less harsh, frequently mixed with spines; tail generally long. One Ethiopian genus, and the remaining nine or so Neotropical. Many of the species are of large size, some being arboreal and others aquatic.

_Myopotamus._[391]—Incisors very large; molars with two internal and two external enamel-folds in the upper, and three internal and one external in the lower jaw, last molar the largest; ears moderate; tail about two-thirds the length of the head and body, scaly, and sparsely haired; hind feet webbed; five digits. Vertebræ: C 7, D 13, L 6, S 4, C 25. The well-known Coypu (_M. coypu_), the only existing representative of this genus, is one of the largest living members of the order, and attains a length of about 2 feet. It is common in South America, living in burrows near water, and feeding on aquatic plants. Fossil remains of the genus occur in the caverns of Brazil, as well as in the Tertiaries of Argentina.

_Capromys._[392]—This genus comprises arboreal forms from the West Indies allied to the Coypu, but, according to Dr. G. E. Dobson, showing signs of affinity with the _Hystricidæ_. The incisors are smaller than in the Coypu, and the upper molars have one internal and two external enamel-folds; the ears are comparatively small; the tail usually of considerable length, and the general form somewhat Rat-like. The typical _C. pilorides_ is somewhat smaller than the Coypu, and is confined to Cuba; it is remarkable for the subdivision of the lobes of the liver into a number of lobules. _C. brachyurus_ and _C. prehensilis_ are also confined to Cuba. In Jamaica the genus is represented by _C. melanurus_, which is somewhat smaller than a Rabbit, and has no secondary lobulation of the liver.[393]

_Aulacodus._[394]—Upper incisors with three deep grooves; molars as in _Capromys_. Fur very harsh; tail moderate, sparsely haired; manus with rudimentary pollex, and small fifth digit; pes with no hallux, and rudimental fifth digit. One species (_A. swinderianus_), from Western and Southern Africa, which attains a length of nearly 2 feet, and dwells in burrows.

_Plagiodon._[395]—Allied to _Capromys_, but with the enamel-folds of the molars very complex, and forming a kind of zig-zag pattern in those of the upper jaw. Represented only by _P. ædium_ of Hayti and Jamaica.

_Loncheres_[396] and _Echinomys_.[397]—These genera include small South American species, in most of which flattened lanceolate spikes are mingled with the fur. The majority of the species occur in Guiana and Brazil, but one species of _Echinomys_ has been recorded from Central America. Fossil remains of both genera occur in the cavern-deposits of Brazil.

_Mesomys._[398]—This genus resembles _Loncheres_ externally, but the pollex has a short curved claw, and there are no spines in the fur.

_Dactylomys._[399]—A Brazilian genus presenting the following distinctive features. Ears short; tail long and scaly; pollex minute; third and fourth digits of manus elongated, with short convex nails. Incisors flat; molars divided into two lobes, each of which has a single enamel-fold. Represented by two species, _D. typus_ and _D. amblyonyx_, both of which seem to be rare and but little known. In the elongation of some of the digits _Dactylomys_ recalls _Chiromys_ among the Primates.

_Cercomys._[400]—This South American genus is usually placed near _Carterodon_, from which it is readily distinguished by the pointed muzzle and the plain incisors.

_Carterodon._[401]—This genus, which was originally described upon the evidence of skulls from the Brazil caves, but subsequently found living, is readily distinguished by the broad and grooved incisors. The upper molars have one inner and two outer enamel-folds; those of the lower jaw being the reverse of this.

_Fossil Forms._—Remains of the existing genus _Loncheres_ occur in the Brazilian cave-deposits, which also yield the extinct _Dicolpomys_. A large number of fossil _Octodontidæ_ from the Tertiaries of South America have been described under many generic names, but it will be sufficient to mention that _Phloramys_ and _Pithanotomys_ are considered to be allied to _Ctenomys_; while _Morenia_, _Orthomys_, and _Trilodon_ show affinity to _Myopotamus_. _Pellegrinia_, from the Pleistocene of Sicily, may be allied both to _Ctenodactylus_ and _Octodon_.

_Family_ THERIDOMYIDÆ.

This extinct family, which is represented in the Tertiaries of Europe and the United States, comprises several genera of comparatively small Rodents, which are regarded by Dr. Schlosser as nearly related to the _Octodontidæ_, although connected by _Archæomys_ with the _Chinchillidæ_. The dental formula is the same as in the _Octodontidæ_. In the typical genus _Theridomys_, from the Lower Miocene and Upper Eocene of Europe, the molars are rooted, and have three or four re-entering enamel-folds, which form isolated discs on the worn crowns. _Syllophodus_, from the Miocene of the United States, is closely allied. _Protechinomys_ and _Trechomys_ are genera from the Phosphorites of Central France with rooted molars; while in _Archæomys_ of the same deposits the molars are rootless, with the enamel-folds dividing their crowns into laminæ, as in the Chinchillas.

_Family_ HYSTRICIDÆ.

Build stout. Limbs subequal. A number of long and stout spines in the integument. Facial portion of skull short and broad, and the jugal without an inferior angle. Molars with external and internal enamel-folds; completely or partly rooted.

Subfamily =Synetherinæ=.—Molars rooted; clavicles complete; upper lip not cleft; soles tuberculated; pollex absent; four mammæ; tail generally prehensile; spines mixed with long hairs. This group is confined to America, all the forms except one being arboreal, and their habits less strictly nocturnal than in the next subfamily. There are three genera.

_Erethizon._[402]—Represented by the common Canadian Porcupine (_E. dorsatus_), a stout heavily-built animal, with long hairs almost or quite hiding the spines; four anterior and five posterior toes; and a short stumpy tail. It is a native of the greater part of Canada and the United States where there is any remnant of the original forest left. Remains of _Erethizon_ occur in cavern-deposits in Pennsylvania.

_Synetheres._[403]—This genus contains some eight or ten species, known as Tree Porcupines (Fig. 214), found throughout the tropical parts of South America, and one of them extending northwards into Mexico. They are of a lighter build than the Ground Porcupines, are covered with short, close, many-coloured spines, often mixed with hairs, and their tails are always prehensile. Their hind feet have only four toes, owing to the suppression of the hallux; but they have a peculiar fleshy pad on the inner side of the foot, between which and the toes boughs and other objects can be firmly grasped as with a hand. Vertebræ: C 7, D 17, L 5, S 3, C 36. An extinct species of this genus has been described from the cavern-deposits of Brazil.

_Chætomys._[404]—Distinguished by the shape of its skull and the greater complexity of its teeth. It contains only one species (_C. subspinosus_), a native of the hottest parts of Brazil.

Subfamily =Hystricinæ=.—Molars semi-rooted; clavicles incomplete; soles smooth; a rudimentary pollex: six mammæ; tail not prehensile. Now confined to the Old World, where they occur in Southern Europe, Africa, India, and the Malay Archipelago as far eastwards as Borneo. Habits terrestrial and nocturnal. Three genera.

_Hystrix._[405]—This genus is readily characterised by the inflated skull, in which the nasal chamber is often considerably larger than the brain-case, and by the short tail, tipped with numerous slender stalked open quills, which make a loud rattling noise when the animal moves. Vertebræ: C 7, D 15, L 4, S 4, C 12. The best-known member is the Common Porcupine (_H. cristata_, Fig. 215), which occurs throughout Southern Europe and North and West Africa, but is replaced in South Africa by _H. africæ-australis_, and in India by the Hairy-nosed Porcupine (_H. leucura_).

The following account of the habits of the last-named species is from Dr. Jerdon: “_Hystrix leucura_ is found over a great part of India, from the lower ranges of the Himalayas to the extreme south, but does not occur in lower Bengal, where it is replaced by _H. bengalensis_. It forms extensive burrows, often in societies, in the sides of hills, banks of rivers and nullas, and very often in the dams of tanks, and in old mud walls, etc. In some parts of the country they are very destructive to various crops, potatoes, carrots, and other vegetables. They never issue forth till after dark, but now and then one will be found returning to his lair in daylight. Dogs take up the scent of the Porcupine very keenly, and on the Nilghiris I have killed many by the aid of dogs, tracking them to their dens. They charge backwards at their foes, erecting their spines at the same time, and dogs generally get seriously injured by their strong spines, which are sometimes driven deeply into the assailant. The Porcupine is not bad eating,—the meat, which is white, tasting something between pork and veal.”

Besides these three large crested species of _Hystrix_, there are four or five smaller species without nuchal crests occurring in North-East India and in the Malay region, from Nipal to Borneo.

Fossil species of _Hystrix_ occur in the Pleistocene and Pliocene of India, and in Europe from the Upper Pliocene to the Middle Miocene, being perhaps also represented in the French Phosphorites. Remains from the Pliocene and Miocene of the United States have been referred to this genus, and if rightly determined are of especial interest from a distributional point of view.

_Atherura._[406]—The Brush-tailed Porcupines are much smaller animals than the last, characterised by their long tails tipped with bundles of peculiar flattened spines. Of the three species two are found in the Malay region and one in West Africa. A fossil species occurs in the cavern-deposits of Madras.

_Trichys._[407]—This genus contains but one Bornean species (_T. guentheri_), externally very like an _Atherura_, but differing from the members of that genus in many important cranial characters.

_Family_ CHINCHILLIDÆ.

Terrestrial forms, with elongated hind limbs, bushy tails, very soft fur, and complete clavicles. Jugal without an inferior angle, and extending forwards to the lachrymal; palate contracted in front and deeply emarginate behind; incisors short, and the molars divided by continuous enamel-folds into transverse laminæ. Neotropical region. This family includes only three existing species, divided into as many genera.

_Chinchilla._[408]—In this genus the fore feet have five and the hind four digits, the tail is long and bushy, and the auditory bullæ are enormous, appearing on the top of the skull. The one species (_C. lanigera_) is restricted to the alpine zones of the Andes from the north of Peru to the south of Chili. It is a Squirrel-like Rodent, about 10 inches in length, the tail somewhat exceeding 5 inches, and the ears very large. Its fur is greatly valued on account of its extreme softness and delicate gray colour.

_Lagidium_[409] and _Lagostomus_.[410]—_Lagidium_ has four digits in both fore and hind feet, and _Lagostomus_ three only in the hind feet, and the auditory bullæ are much smaller than in the preceding genus. _Lagidium_ has the same distribution as _Chinchilla_; while _Lagostomus_, as represented by the Viscacha (_L. trichodactylus_), is found in the Pampas from the Uruguay River to the Rio Negro. The Viscachas live in burrows, generally in large numbers, and are nocturnal in their habits. Remains referable to the existing species, as well as others which appear to belong to extinct forms, occur in the Pleistocene deposits of South America.

_Extinct Genera._—Several Rodents from the South American Tertiaries more or less closely allied to _Lagostomus_ have been described by Dr. Ameghino under the names of _Prolagostomus_, _Pliolagostomus_, etc. The huge _Megamys_ (_Potamarchus_), from the infra-Pampean deposits of Parana and Patagonia, is referred to this family, and has dimensions approximating to those of an Ox. Other fossil genera have received the names of _Epiblema_ and _Tetrastylus_.

_Family_ CASTOROIDIDÆ.

_Castoroides._[411]—The large Beaver-like Rodent with the dimensions of a Bear from the Pleistocene of the United States described under this name is regarded by Dr. Coues as the type of a family. Its dentition is nearest to that of _Chinchilla_ and _Hydrochœrus_, but some of the cranial characters are like those of the _Castoridæ_. The genera _Amblyrhiza_ and _Loxomylus_, from the Pleistocene of the Antilles, appear to be allied types.

_Family_ DASYPROCTIDÆ.

Terrestrial forms with subequal limbs, hoof-like claws, short or obsolete tail, and rudimentary clavicles. Mandibular masseteric ridge obsolete; palate broad; incisors long; molars semi-rooted, with external and internal enamel-folds. Neotropical region.

_Dasyprocta._[412]—Includes several slender-limbed species, with three hind toes, commonly called Agoutis, inhabiting Central and South America, one (_D. cristata_) extending into the West-Indian Islands. Numerous fossil remains of this genus occur in the cavern-deposits of Brazil.

_Cælogenys._[413]—This genus is readily characterised by the presence of five hind toes, and the extraordinary development of its zygomatic arches, which are enormously expanded vertically, forming great convex bony capsules on the sides of the face, enclosing on each side a large cavity lined with mucous membrane, and communicating by a small opening with the mouth. The Paca (_C. paca_) is about 2 feet long, and, like the species of _Dasyprocta_, lives generally in the forests or along the banks of rivers. This species appears to date from the epoch of the Pleistocene deposits of the Brazilian caves. A smaller species from Ecuador, living at elevations of from 6000 to 10,000 feet, has been described as _C. taczanowskii_.

_Family_ DINOMYIDÆ.

Distinguished from the _Dasyproctidæ_ by the cleft upper lip, rather long and bushy tail, the presence of four digits in both fore and hind feet, and the complete clavicles. The manubrium is broad; the optic foramina are confluent; the incisors broad; and the molars rootless, with enamel-folds dividing them into transverse laminæ.

_Dinomys._[414]—The sole representative of this family is the Rodent known as _D. branicki_, of which hitherto only a single specimen has been obtained. This was captured in Peru, where it was found at daybreak walking about a courtyard; the inhabitants of the district were previously unacquainted with the species, from which its extreme rarity may be inferred. Externally it resembles much the Paca, having similar S-like nostrils; but in the laminated molars, and many features of the skeleton, it differs from all the other Rodents with hoof-like nails. It is regarded by its describer, the late Professor Peters, as a connecting link between the _Octodontidæ_, _Chinchillidæ_, _Dasyproctidæ_, and _Caviidæ_.

_Family_ CAVIIDÆ.

Terrestrial or natatorial forms, with short incisors, strong mandibular masseteric ridges, long and curved paroccipitals, and palate contracted in front. Fore feet with four digits, hind feet with three. Clavicles imperfect. Molars divided by enamel-folds into transverse laminæ; milk-teeth shed before birth. Other characters as in _Dasyproctidæ_. Neotropical region.

_Cavia._[415]—Limbs and ears short, subequal; tail none. Vertebræ: C 7, D 13, L 6, S 4, C 7. This genus includes several species widely distributed throughout South America, extending even to the Straits of Magellan. The Restless Cavy (_C. porcellus_), which is found throughout Uruguay and Brazil, has been very generally regarded as the ancestral form of the domesticated Guinea-Pig. It is about 10 inches long, and weighs a little over a pound; its fur is long and of a nearly uniform grayish-brown colour. This species is rarely found in dry sandy localities, preferring marshes covered with aquatic plants, among which it lies concealed, feeding in the early morning and after sunset in the evening; but when the soil is dry it forms burrows. It lives in societies of from six to eighteen individuals, breeding but once a year, with one, or at most only two, young at a birth. The Guinea-Pig (probably a misnomer of Guiana-Pig) is larger than _C. porcellus_, and is regarded by Dr. Nehring as descended from another species, _C. cutleri_. It is white in colour, with irregular patches of reddish-brown and black. The Bolivian Cavy (_C. boliviensis_), found throughout the higher regions of Bolivia, usually at an elevation of 10,000 or 12,000 feet, is exceedingly shy, and lives in burrows, which in some districts are so numerous as to have completely undermined the soil. The Rock-Cavy (_C. rupestris_), distinguished by its short, blunt nails, is found in rocky situations throughout Brazil, and is much sought after for its flesh. The Southern Cavy (_C. australis_), common along the coast of Patagonia, forms deep burrows, with several outlets, in sandy declivities. Remains of existing species of _Cavia_ are found in the cavern-deposits of Lagoa Santa, Brazil.

_Dolichotis._[416]—Characterised by the great length of the ears and the short tail. The palate is so much contracted in front that the premolars of opposite sides touch by their antero-internal edges. Vertebræ: C 7, D 12, L 8, S 3, C 10.

The Patagonian Cavy (_D. patachonica_)—the only living representative of the genus—is rather larger than a Hare, which it somewhat resembles in external appearance. It inhabits the dry sterile districts of Patagonia and La Plata, disappearing wherever the country becomes more humid. This animal burrows in the earth, although in districts where the Viscacha is found it is said to avail itself of the works of the latter. Unlike other cavies, its eyes are protected from the glare of the sun by prominent eyelashes. The body is covered with a long dense fur of a rusty colour. Two young are produced at a birth. Three species of _Dolichotis_ have been described from the Brazilian cave-deposits, one of which is probably not really separable from the existing form.

_Hydrochœrus._[417]—A large aquatic form with all the feet fully webbed; the skull (Fig. 213, p. 481) large, with enormous paroccipital processes; and the molars very complex, the third upper one having some twelve transverse laminæ. Upper incisors grooved. Vertebræ: C 7, D 14, L 6, S 3, C 8.

The Capybara (_H. capybara_) is the largest existing Rodent, and the only living representative of the genus. It is a bulky and stoutly built animal, and attains a length of about 4 feet. The body is covered with long and coarse hair, reddish-brown above and brownish-yellow beneath. Capybaras are found over the whole of the eastern part of South America, and to the westward range into Bolivia and Peru. They frequent the borders of rivers and lakes, concealing themselves among reeds and other water plants. Remains of _Hydrochœrus_ are found in the cavern-deposits of Brazil, which are probably referable to the existing species; one extinct species from the Pleistocene of Buenos Ayres is estimated to have attained a length of 5 feet, while _H. magnus_ of the same deposits was of still larger dimensions. The genus is also represented in the Pleistocene of South Carolina and the infra-Pampean beds of Parana.

_Extinct Genera._—A number of South American fossil Rodents have been referred to extinct genera of _Caviidæ_. Thus _Plexochœrus_, from the Tertiary of Argentina, differs from _Hydrochœrus_ in having only nine laminæ in the last upper molar; _Cardiomys_, _Cardiatherium_, etc., from the infra-Pampeans are also stated to be allied to _Hydrochœrus_, while _Contracavia_, of the same deposits, is related to _Cavia_, but of larger size. _Microcavia_, again, from the Pleistocene of Argentina, is regarded as connecting _Cavia_ with _Dolichotis_. The Tertiary European genera _Issiodoromys_ and _Nesocerodon_ are apparently referable to the present family.

_Suborder_ DUPLICIDENTATA.

Two pairs of incisors in the upper jaw (the second very small, and placed directly behind the large first pair), the enamel of which extends round to their posterior surfaces. At birth there are three pairs of these incisors, but the outer one on each side is soon lost. Incisive foramina large; and usually confluent; bony palate very narrow from before backwards; no true alisphenoid canal; fibula ankylosed to the tibia, and articulating with the calcaneum. Testes permanently external. This suborder includes the Picas, Hares, and Rabbits, all of which are strictly terrestrial.

_Family_ LAGOMYIDÆ.

Complete clavicles, subequal limbs, no external tail, and short ears. Skull depressed, frontals contracted and without postorbital processes; _p_ ¹⁄₁ or ²⁄₂; molars rootless, with transverse enamel-folds. Palæarctic and Nearctic.

_Lagomys._[418]—Represented by about a dozen species of small Guinea-Pig-like animals, inhabiting chiefly the mountainous parts of Northern Asia (from 11,000 to 14,000 feet), one species only being known from South-East Europe, and another from the Rocky Mountains.

The Picas, or Tailless Hares, live in holes among the rocks of their native mountains, and are agile and shy little creatures. The genus is well represented through the upper and middle Tertiaries. It has been proposed to separate those fossil forms with _p_ ²⁄₁ as _Myolagus_, and those with _p_ ¹⁄₁ as _Titanomys_, but this seems scarcely advisable.

_Family_ LEPORIDÆ.

Imperfect clavicles, elongated hind limbs, short recurved tail, and long ears. Skull (Fig. 216) compressed, frontals with large wing-shaped postorbital processes _p_ ³⁄₂; molars as in the _Lagomyidæ_. Cosmopolitan (except Australasia). Vertebræ: C 7, D 12, L 7, S 4, C 13-15.

_Lepus._[419]—The single genus _Lepus_ includes about twenty species, all of which resemble one another in general external characters. In all the fore limbs have five and the hind only four digits, and the soles of the feet are densely clothed with hairs similar to those covering the legs; the inner surface of the cheeks is also hairy. Although the family has such a wide distribution, the greater number of the species are restricted to the Palæarctic and Nearctic regions, only a single species (_L. brasiliensis_) extending into South America, where it has existed since the date of the Pleistocene deposits of the Brazilian caves.

The Common Hare (_L. timidus_[420]) may be taken as a typical example of the genus, and is characterised by the great length of the ears and hind limbs. It is found in all parts of Europe except the north of Russia, the Scandinavian peninsula, and Ireland. Its fur is usually of a tawny gray colour above and white beneath, with the upper surface of the short tail and the tips of the ears black. The colour of the fur differs, however, considerably in different latitudes and at different seasons of the year; showing a tendency to become white during winter in northern countries, while assuming a reddish-yellow hue in the more genial climate of southern Europe. The Hare is a nocturnal animal, remaining during the day on its “form,” as the slight depression is called which it makes in the open field, usually among grass.

The Mountain Hare (_L. variabilis_) is found throughout the northern part of the Palæarctic region, ranging from Ireland in the west to Japan in the east, and also occurring in several of the more southerly mountain ranges, such as the Pyrenees, the Alps, and the Caucasus. It is smaller than the common species, with a smaller and more rounded head, and shorter ears, tail, and hind limbs. In cold climates the colour of the whole animal changes in the winter to a pure white (as in Fig. 218), with the exception of the tips of the ears, which remain black. In Ireland no winter change of colour takes place.

The Rabbit (_L. cuniculus_), speaking of the wild race only, is distinguished from the Hare externally by its smaller size, shorter ears and feet, the absence or reduction of the black patch at the tip of the ears so characteristic of the Hare, and by its grayer colour. The skull is smaller and lighter, with a slenderer muzzle and a longer and narrower palate. Besides these characters, however, the Rabbit is sharply separated from the Hare by the fact that it brings forth its young naked, blind, and helpless; to compensate for this, it digs a deep burrow in the earth in which they are born and reared, while the young of the Hare are born fully clothed with fur, and able to take care of themselves in the “form” in which they are born. The weight of the Rabbit is from 2½ to 3 lbs., although individuals perfectly wild have been recorded up to more than 5 lbs. Its general habits are too well known to need a detailed description here. It breeds from four to eight times a year, bringing forth each time from three to eight young. Its period of gestation is about thirty days, and it begins to breed when six months old. It attains to an age of about seven or eight years.

The geographical distribution of the Rabbit presents many most interesting peculiarities. It is believed to be originally a native of the western half of the Mediterranean basin only, and still abounds in Spain, Sardinia, Southern Italy, Sicily, Greece, Tunis, and Algeria; and many of the Islands adjoining these countries are quite overrun with it. Thence it has spread, partly by man’s agency, northwards throughout temperate Western Europe, increasing rapidly wherever it gains a footing; and this extension is still going on, as is shown by the case of Scotland, in which sixty years ago Rabbits were little known, while they are now found in all suitable localities up to the extreme north. It has also gained admittance into Ireland, and now abounds there as much as in England. Out of Europe the same extension of range has been going on. In New Zealand and Australia Rabbits, introduced either for profit or sport, have increased to such an extent as to form one of the most serious pests that the farmers have to contend against, as the climate and soil seem to suit them perfectly, and their natural enemies are too few and too lowly organised to keep their numbers within reasonable bounds. In other cases Rabbits introduced into islands have become or remained more or less distinct from their parent stock; thus the Rabbits both of the Falkland Islands and of Jamaica still show traces of their descent from domesticated varieties, and have never reverted to the ordinary brownish-gray type. And again, as was pointed out by Mr. Darwin,[421] the Rabbits in the island of Porto Santo, near Madeira, whose ancestors were introduced from Spain in 1418 or 1419, have formed quite a distinct diminutive race, barely half the bulk or weight of English Rabbits, and differing in certain slight details of colour and habits.

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